Gardeners talk a lot about amending soils for plants in their beds and borders and this is generally a good thing, however, trees are a separate matter. The root zone of most trees spreads out at least as far as the height of the tree. That is, for a 100 foot tall tree, the root system could spread out up to 100 feet in all directions under optimum conditions. A few species will send roots out even further while some, like spruce trees, will not spread roots nearly so far on average.

Another thing to consider is that the vast majority of the roots of trees and shrubs go out horizontally. By far the bulk of roots of these plants are found in the top 18 to 24 inches of soil. Why? Because that is where the water and nutrients are located. There are certainly some roots that go deep into the ground to help anchor the tree and there are some species that send down a true taproot. However, the roots that the tree depends on for survival are near the soil surface.

On a practical basis, it would be impossible to amend enough soil to account for a tree's mature root zone. Therefore, they must survive in the native soils alone without any amendments like peat moss or compost. If your soils are heavy clay or extremely light sand, you have a problem or, at least, a challenge. No doubt about it. In these cases, we just have to use some techniques that allow us to do the best we can and then leave it up to the plant to survive...or not.

A. Planting Trees in Standard Soil Conditions - Many garden soils are a somewhat uniform mixture of sand, silt and clay and fall into what is commonly called a "loam" soil type. Such soils have good drainage and there is no evidence of ponding or puddling after a summer storm. Water drains off quickly leaving the soil moist but not waterlogged. Also, these soils are not excessively sandy which would cause water to disappear too rapidly and would be considered droughty. These favorable characteristics would result in what we might call a "standard" or "typical" soil for many home landscapes.

In these kinds of general conditions, the rule about planting at the same depth as the plant was growing at its previous site applies most of all. If the root ball of the tree is 12 inches high, dig a hole that is12 inches deep and as wide as you can reasonably go. Then take the shovel and loosen the soil to about that depth out to the sides of the root ball. This will add air to the soil and encourage tree roots to grow laterally over the coming years.

B. Planting Trees in Heavy Clay Soils - The exception to the general planting depth rule is to plant trees "high" in poorly drained clay soils. Here, we are trying to make the best of a bad situation. If you are one of those super rich gardeners, you could consider changing huge amounts of soil throughout the entire potential root zone of the tree. For most of us common folks, however, we will just have to make the best of the soil we have on our site.

In clay soils, if we dig a standard type of hole, it may form what is called the "bathtub effect". In this case, especially if the clay is wet when being dug, the sides of the hole will be slick like the ceramic coating on a bathtub. It will dry very hard and rainwater will sit in the hole for days and days before very slowly draining away. In this situation, at the very least, the roots will not expand and at the worst, they will rot away.

In heavy clay soils, we will dig a saucer shaped hole that is shallow and as wide as we can make it. If the root ball is 12 inches tall, we might dig the hole 8 or 9 inches deep. Then, when the soil that was taken from the hole is replaced, it will form a bit of a slope away from the trunk of the tree. This will allow for a certain amount of surface drainage. By making the hole as wide as you can, the roots will be encouraged to expand out horizontally into the newly disturbed soil.

Since the root ball is standing above the regular soil level a bit, this is one case where staking may be needed to keep the tree from falling over in the breeze. We cover staking later in this eBook.

C. Planting Bare Root Trees - Trees or other woody plant material that come to you bare root should be planted as soon as possible after delivery. The day before you plant, you should put the roots of the tree in a pail of water so that it can replenish its supply.

Follow the relevant depth rules discussed in A & B above depending on the type of soil. In the bottom of the hole, build a mound in a cone shape and spread the roots out on top of it. You can add or subtract some soil from the cone until the trunk is at the proper height above the soil line.

Loosen the soil on both sides of the hole to the correct depth. Then, fill the hole with soil that came out of during excavation. Water the area near the trunk thoroughly to remove any large air pockets that might be trapped in the soil.

D. Planting Balled and Burlaped Trees - Follow the relevant depth rules discussed in A & B above depending on the type of soil. The key factor with planting B&B nursery stock is that it is very important to cut and/or remove all ropes, wires and strings used to hold the ball together once the plant is in the hole. If any are wrapped around the base of the trunk, it is imperative that these be cut or as the tree grows in girth, it may be girdled and die within a few years after planting. Sometimes the strings will be called "biodegradable" and this may be true. However, it is not worth taking the long-term risk. Cut them all!

Loosen the soil on both sides of the hole to the correct depth. Then, fill the hole with soil that came out of it during excavation. Make sure that the burlap is buried beneath the soil surface or this will act as a wick and take moisture away from the roots. Irrigate the area near the trunk thoroughly to remove any large air pockets that might be trapped in the soil.

E. Planting Container Grown Trees - Follow the relevant depth rules discussed in A & B above depending on the type of soil. Since the plants have been growing in the container for a year or more, they should have built a solid root mass. Often, the roots have completely filled the container and some of them may be circling around the inside of the pot. If you just plop this root mass into the soil, those roots will continue to grow in a circle and may eventually wrap around the trunk. That can girdle the trunk and result in the death of the tree. Unfortunately, this may not happen for as much as a decade or more after the date of transplant.

So, it is important to take a sharp tool of some sort and cut those circling roots. It is also vital that you cut through the matted roots on all four sides and cut in a cross shape across the bottom of the root mass.

Loosen the soil on both sides of the hole to the correct depth. Then, fill the hole with soil that came out of during excavation. Water the area near the trunk thoroughly to remove any large air pockets that might be trapped in the soil.

While concentrating on the proper depth of planting is very important, don't forget to take a look at the above ground portion of the tree too. Be sure that the branches of the canopy are properly aligned for maximum viewing and proper growth. Also, be sure the trunk is perpendicular with the ground before you refill the hole.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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